I'll take a stab at it:
1. During most of homo sapiens evolution as hunter gatherers, women were more likely to congregate in centralized groups while men hunted in small groups. It is documented that gossip is an integral activity among the women of a tribe moreso than their male counterparts. Without the inhibitions produced by in-person interaction, women gossiping on social media are more likely to produce negative interactions than their male counterparts who have a much lessened propensity to gossip.
2. From an evolutionary standpoint, a woman's reproductive fertility is closely associated with their appearance. Men are hardwired to pay close attention to a woman's looks whereas women are hardwired to care more about a man's ability to "protect and provide". Since social media promotes visibility of the most attractive women, this has the effect of reducing feelings of self-worth for the female users moreso than the male users.